Bound by Silicone - roeloffze dental laboratory

The sticky relationship between Dentists and
Dental Laboratories
Mark Jackson, RDT
Precision Ceramics Dental Laboratory, DAMAS
Montclair, CA
The Dentist and the Dental Lab
According to the FDA, the Dental Laboratory is a Medical Device Manufacturer and
subject to FDA Good manufacturing Practices…..
But things haven’t always been like this!
During the middle ages
and throughout the 19th
century, dentistry was
not a profession in itself,
and often dental
procedures were
performed by barbers or
general physicians.
Barbers usually limited
their practice to
extracting teeth which
alleviated pain and
associated chronic tooth
infection.
At the turn of the
century, most dentists
were expected to make
their own dentures
crowns and bridges,
but by the 1900’s the
dentists realized the
economic benefits of
finding specialized
help.
Professional relations
were best summarized
in two simple words:
“Yes Doctor.”
The “Plaster Monkey”
was actually a term of
endearment, and the
“dental mechanic”
became an important
member of the dental
team, though dentists
still kept them closely
supervised….and
undereducated.
Dental Technicians were
forbidden to attend
lectures and meetings,
and in 1963, the NADL
and ADA broke off
relations.
It was a contentious
time.
Today’s credentialed
technicians have
strong backgrounds in
material science,
dental anatomy and
CAD/CAM technology,
and in some cases can
earn more than a
general dentist.
Despite some
professional growing
pains, and some
sibling rivalry, we
share a relationship
that is mutually
beneficial, financially
rewarding and based
on a shared respect.
HOWEVER….
Our Relationship is held together by
a third party
The dental impression is the key ingredient in our relationship, and can often
make or break it. We depend on the quality, consistency and the technical
support provided by our impression material manufacturers.
Impressions are the foundation
of everything we do.
It all starts with a great impression....
But usually not…..
More than 50% of the impressions we
receive are substandard, yet only
1-2% will be returned
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Proper tray selection
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Proper use of tray adhesive

Material properly mixed

Adequate volume of material

Adequate adhesion between
materials

No pressure points or tray pinching

No teeth contacting the tray

Good detail of margin (finish line)

Good detail of prepared teeth

No voids or pulls in the material that
will cause interference

While this impression displays a
number of problems, it was clearly
the improper tray for this
application. Improper tray selection
can cause tray flex and rebound.

This tray had no adhesive at all, and
also shows signs of possible tray
distortion. Tray adhesives are
specifically formulated and not
interchangeable.

With modern impression delivery systems,
mixing problems have been all but eliminated,
however glove contamination and chemicals
can inhibit polymerization and setting
resulting in tacky washed out appearance.

Improperly filled impression trays
can result in missed anatomical
features or movement of the
material within the tray borders

Inadequate adhesion between
different impression materials can be
caused by contamination, exceeding
the working time or improper
storage of material.

This tray was either not positioned
properly, or was the wrong size. When
this happens, the tray can flex and
spring back, distorting the impression,
or in the best case hold the bite open.

Like the previous example of a pressure
point, this tray was either the wrong
size, or improperly positioned, but
instead of a soft tissue compression, we
have tooth-on-tray contact.

Poor gingival retraction and
syringing technique.

Not bleeding the mixing tip or
poor syringing technique has
resulted in air folding or
entrapment

Insufficient retraction or tearing

Improper retraction, possible fluid
or chemical contamination

Improper retraction allowing blood
or saliva to pool around the
prepared tooth. Exceeding working
time.

This impression has voids and pulls
caused by exceeding working time,
moving the tray after seating, or not
enough material. These defects can
interfere with occlusion and mounting
models
Evaluating remakes

Every impression
would be a perfect
one, that had been
inspected by the
dentist, and was
free of the defects
we just discussed,
but that is rarely
the case….

Most dental
laboratories have a
profit margin of
10% or less. That
means they may
have to do as many
as 19 units at no
profit to pay for a
single remake.

Every remake is
evaluated to
determine the
nature of the
failure. In some
cases it is
laboratory error or
product failure, and
sometimes it is
doctor error.

The easiest way to
see if the
impression was the
problem is to
simply insert the
new die into the old
impression and
look for the
discrepancy.

A common problem
is misreading the
margin, usually
caused by a bad
impression, though
technician error
does happen too.

Frankly, the lab
takes some blame
due to errors in
mixing stone,
applying surfactant
or surface
disinfectants,
though we try to
automate these
processes when
possible.

But in an
overwhelming
number of cases
the problem can be
traced back to a
bad impression. In
some cases we
accepted them
when we really
should have sent
them back.
And it’s even less likely there
will be time to do it over!
This is where many of
us revert back to our
primordial roots, avoid
confrontation and “do
our best” at the
doctors instruction
We take the “passive aggressive”
approach…
The “habitual offender” card

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Carefully inspect your impression before releasing your patient. Any pull, voids,
bubbles, unset or sticky material indicates contamination or a mixing problem.
This will lead to a remake.
If you use a desensitizing substance on prepared teeth, apply it AFTER taking
your impression. These substances effect impression materials and if used
improperly will guarantee a remake.
Retraction cord containing epinephrine, or other material containing
epinephrine will cause deterioration, sticky or unset margins in some
impression materials. AGGRESSIVELY rinse and clean the prepared teeth before
injecting your wash material.
Materials containing Ferrite sulfate will cause some impression materials to not
set properly, especially in thin areas such as margins. Save yourself a remake;
clean and rinse your preps well before taking the impression
If you are using “sideless” triple trays, PLEASE check to see that the patient did
not bite into, or onto the tray. If they did, when we mount the models, the bite
will be off, and you will lose precious time adjusting the occlusion and possibly
ruining the crown, or sending it back for repairs. A preliminary check could save
hundreds of dollars later.
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PLEASE take some time to make sure your temporaries are in occlusion, and that contacts are tight.
For long span bridges, or cosmetic make-overs, consider our lab processed temporaries. Believe it
or not, we have seen three and four unit bridge cases with single crown temporaries on the
abutments. That’s a great way to guarantee your bridge will NOT fit!
We recommend a two cord technique. A combination of #00 and #2 cords will provide adequate
retraction for nice clear exposure of your margins.
For anterior cases, please send an impression of the temporaries, or a diagnostic wax up, so that we
can try and match patient expectations. Photos, shade maps and other tools will ensure a happy
patient and a happy doctor.
When injecting wash impression around the margins, use a stirring motion and “jiggle” the material
constantly to avoid air bubbles or voids. Never stop and restart an impression. If you don’t think the
cartridge has enough material left to completely encircle the prep, use a new cartridge. If the case
has loose tissue, of if the prep is very subgingival, use the cartridge tip to push the tissue away as
you inject the material to prevent it from laying over onto the margin.
DO NOT use the “touch” technique to determine if your impression is set; use an inexpensive egg
timer or other timing device. The manufacturer has done extensive tests to determine the best
setting time and conditions. The material you are touching has been exposed to air, and may set
before the was material has, and it is important to have this part intact and accurate. Don’t touch;
thime it or you may end up remaking it.
All crown preps should have adequate prep reductions of at least 1.5 mm for both PFM and All
Ceramic Crowns.

Note: 7 out of 10 tips are impression related!
Kerr Rep
We call in reinforcements!